1. Field of the Invention
The present invention relates to a compressor control system for a vehicle air conditioner. In the compressor control system, an electric motor for driving a compressor is controlled by a driving electronic control unit that controls a driving of the vehicle.
2. Description of Related Art
In a conventional air conditioner (e.g., JP-A-2000-318435) of a vehicle such as a hybrid vehicle and an electric vehicle, a compressor in a refrigerant cycle system of the air conditioner is driven by an electric motor. Here, the hybrid vehicle is a vehicle which drives while a driving mode is switched between a battery driving mode by an electric motor and an engine driving mode. The electric vehicle is a vehicle which drives only by using a battery.
As shown in FIG. 11A, the above air conditioner includes an air-conditioning electronic control unit (ECU) 107. The air-conditioning ECU 107 controls operation of interior air-conditioning components of the air conditioner. Specifically, the air-conditioning ECU 107 controls a rotation speed of a compressor electric motor 47 through a compressor inverter 48, so as to control a compressor 41.
Although not shown in the above patent document of JP-A-2000-318435, the air-conditioning ECU 107 generally includes devices such as a microcomputer 107a, an input circuit and an output circuit 107c. The output circuit 107c outputs a driving signal for driving the compressor electric motor 47 based on an output signal from the microcomputer 107a. 
An air conditioner shown in FIG. 11B is mounted in an engine vehicle which drives only by an engine. In this air conditioner, a compressor 41 is also driven only by the engine. Therefore, a rotation speed of the compressor 41 is dependently determined by a rotation speed of the engine. Accordingly, the compressor 41 is intermittently driven by controlling an electromagnetic clutch 49 which transmits motive power of the engine to the compressor 41. Otherwise, the compressor 41 is driven by controlling an electromagnetic valve (not shown), so that a discharge amount of the compressor 41 is adjusted. In this air conditioner, an air-conditioning ECU 107′ includes an output circuit 107c′, which outputs a driving signal to the electromagnetic clutch 49, or an output circuit which outputs a driving signal to the electromagnetic valve.
Accordingly, the hardware structure of the air-conditioning ECU 107, which is used for the hybrid vehicle or the electric vehicle and includes the output circuit 107c for outputting the driving signal for the compressor electric motor 47, is quite different from that of the air-conditioning ECU 107′, which is used for the engine vehicle and includes the output circuit 107c′ for outputting the driving signal for the electromagnetic clutch 49 or the electromagnetic valve.
In some cases, the hybrid vehicle or the electric vehicle is manufactured based on the engine vehicle. In this case, existing parts of the engine vehicle are used as much as possible in order to reduce design cost. However, the air-conditioning ECU 107′ for the engine vehicle cannot be used as the air-conditioning ECU 107 for the hybrid vehicle or the electric vehicle without a hardware change. Therefore, the hardware design of the air-conditioning ECU 107′ needs a substantial change, in order to be used for the air-conditioning ECU 107.